Sadly, my husband tells me we did go inside the Pantheon when we were in Rome 8 years ago.  I have no memory of it.  So clearly for me it was not spectacular.

But I do wonder if I've just seen soooo many photographs of it *looking* spectacular that I can't separate those photos from my real experience?  

I do recall, vividly, how much the Colosseum scared and sickened me.  It's like I could feel/smell/see the blood of all the people killed for sport in it.  I couldn't wait to get out of there.

Beside the obvious sunlight shining through the oculus, I personally find the experience at Pantheon more fascinating having studied the building indepth, everything from its history, technological advancements, material use, construction methods to all the changes its been through.

1. you should really go to judge for yourself.

2. my personal experience is similar to access... the fact that it has stood for so long, the fact that someone figured out how to make that dome with an oculus out of those materials so long ago is what is thrilling to me.... it's more the history than how it is now... especially since it looks nothing like what it must have looked when initially completed with all of the stone stripped off the outside (similar to the Colosseum).

I found it to be unspectacular, at least on the inside. In our time, with steel and such, the building just seems ordinary. Sure, for centuries it was an amazing feat of engineering, but without never having experienced a sports stadium, or the like, it's forgettable. The portico and doors, however, WERE memorable. I have never seen doors as large, rustic, robust, and beautiful as the doors on the pantheon. Same with the wooden beams in the ceiling outside. Those are things that we can't experience today.

Don't forget to sit in on a church service in the Pantheon..  The acoustics when the choir sing is unreal. 

When you start learning about the Pantheon, you start being truly amazed.  I sure wouldn't think the oculus was 30' wide standing below, or that its 140' tall, or about its complex filtration system to drain rain water on the floor or that it was linked to a public bath etc etc.

I have been to the Pantheon several times over the years. For me, it truly is a fascinating building and, given its age, a spectacular feat of design. However, it's not always fun being inside the building, especially a) when it's cold and rainy, or b) when the crush of the crowd makes experiencing the space a bit of a challenge.

It's impressive for what it is and when it was built, not to mention the detailing, especially inside.  But it's easy to forget that.  It doesn't take long to see.  And, clearly, the hole in the roof is not effective at screening out the elements.

In that general area, it's much nicer to sit on the Spanish Steps with a gelato in hand on a comfortable summer evening and do some people watching.  The world is in attendance.